Common problem when an airplane, that has already been fueled for a long flight, is swapped to a short flight. You can takeoff (though not leagally) with all the extra fuel but you'll be over your max landing weight at your destination and won't be able to legally land.

Defueling is a slow process. It relies on the aircraft's fuel pumps to push the fuel from the tanks to the truck. Those pumps are sized to pump a bit faster than the engines can draw which is very slow for defueling.

Defueling is also problematic because you are potentially pumping contaminate from the aircraft tanks into the fuel truck so that fuel has to be segregated from the fuel that is going to be pumped into other aircraft. It often takes some time for the fuel vendor to get a defueling truck to the airplane.

Luckily, it doesn't happen too often. In 10+ years, I've defueled maybe twice. I clearly remember once in Miami and think there was probably one other instance.